Hydrogen produced by water electrolysis, and electrochemical batteries are widely considered as primary routes for the long- and short-term storage of photovoltaic (PV) energy. At the same time fast power ramps and idle periods in PV power generation may cause degradation of water splitting electrochemical (EC) cells. Implementation of batteries in PV-EC systems is a viable option for smoothening out intermittence of PV power. Notably, the spreading of. Hydrogen produced by water electrolysis, and electrochemical batteries are widely considered as primary routes for the long- and short-term storage of photovoltaic (PV) energy. At the same time fast power ramps and idle periods in PV power generation may cause degradation of water splitting electrochemical (EC) cells. Implementation of batteries in PV-EC systems is a viable option for smoothening out intermittence of PV power. Notably, the spreading of PV energy over the diurnal cycle reduces power of the EC cell and thus its overpotential loss. We study these potential advantages theoretically and experimentally for a simple parallel connected combination of PV, EC, and battery cells (PV-EC-B) operated without power management electronics. We show feasibility of the unaided operation of PV-EC-B device in a relevant duty cycle and explore how PV-EC-B system can operate at higher solar-to-hydrogen efficiency than the equivalent reference PV-EC system despite the losses caused by the battery.••••Battery cell implemented in photovoltaic-assisted water splitting device.••Feasibility of continuous water splitting without power electronics.••Spreading of light energy over diurnal cycle reduces overpotential in water splitting.••Improved solar-to-hydrogen efficiency despite battery losses.Battery implemented in cell-to-cell photovoltaic assisted water splitting systemContinuous water splittingUnaided water splittingReduction of overpotential lossPV photovoltaic cell or moduleEC electrochemical cellB batteryPV-EC combined device with PV directly connected to ECPV-EC-B combined device with PV directly connected in parallel to EC and BSTH According to the “Global energy system based on 100% renewable energy” report, Photovoltaics (PV) is expected to cover 69% of total primary energy generation in the global renewable energy system in the future. This will require large amount of storage to stabilize power supply. It is expected that short term storage of PV energy will be covered by electrochemical batteries, and long term storage by solar fuels, such as hydrogen produced by water electrolysis. Combinations of PV devices with electrochemical (EC) cells for water splitting [,,,,,,,,,, ] or with batteries (B) [,,,,,, ] have been widely addressed in the literature. It has been found in particular, that intermittent nature of PV power generation with fast power ramps and idle periods cause degradation of water electrolyzers. Implementation of batteries in PV-electrolyzer systems is beneficial to smoothen PV power fluctuation and stabilize performance of the EC components as demonstrated on residential PV system scale. In our previous works we addressed integration of PV cells with EC water splitting cells (PV-EC) [8,11,22] as well as PV-battery integration (PV–B) [,,, ] at cell-to-cell level. In both cases PV cells are directly integrated/connected to an EC or a battery. In this work we investigate behavior and performance of a system with a PV cell directly coupled to an EC cell and a battery (PV-EC-B device). All elements are connected in parallel without power management ele.
